1. Field of the Invention
The present invention relates generally to an ink jet printing apparatus, and more particularly, to a cleaning or housekeeping system within an ink jet printing apparatus which system employs available wiper blades to clean the ink jet printheads.
2. Brief Description of Prior Developments
Basically an ink jet printing apparatus ejects ink from an opening such as a nozzle or an array of nozzles in the form of an image onto a recording medium. The ink can be ejected by an electronic system (i.e. piezoelectric) using a piezoelectric element and an oscillation pressure or one can eject ink as a thermal ink jet system, i.e. using pressure generated as a result of forming and growing bubbles by heat. In either case, by using either method, a high precision image on a recording material can be obtained. Ink jet printing has been used as the means for printing in many different and varied types of apparatus including general printers, facsimile machines, plotters, and postage meters.
Ink jet printing systems generally are of two types, i.e. continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is breaks up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field, which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or to a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with information from digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle or an array of nozzles on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle or an array of nozzles on one end and a heat-generating resistor near each nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. The droplet ejection system based upon thermally generated bubbles is commonly referred to as the xe2x80x9cbubble jetxe2x80x9d system.
In all of the various type of ink jet printing systems as described above, the ink jet printing apparatus employs a cleaning or housekeeping system which is used to clean the ink jet printheads thereby allowing the printheads to function correctly and print at the highest levels of print quality as possible in an ink jet printing system. For example, if not cleaned properly, ink left on the printhead or within the nozzles in the printhead, will dry, especially when the printhead is not in operation, thereby clogging the nozzles and seriously effecting print quality in a negative way.
Generally speaking, a cleaning station sometimes called a housekeeping or service station is used in combination with an inkjet printing system for cleaning the printheads. In the cleaning operation, the printheads are moved over the housekeeping station for maintenance purposes. These housekeeping stations generally include a capping system, which is basically a cap, or caps used with an effective seal to substantially seal the printhead nozzles from contaminants and drying during periods of storage or non-printing. The nozzles in a printhead can be cleaned during operation by sending a number of drops of ink through each of the nozzles by a procedure known as xe2x80x9cspittingxe2x80x9d. In this procedure the waste ink is collected in a xe2x80x9cspittoonxe2x80x9d, i.e. a reservoir in the housekeeping station. In addition to the described spitting and capping procedures for cleaning ink jet printheads, elastomeric wiper elements are also used to wipe the printhead surface to remove ink residue, dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative notion of the printhead and wiper, by, for example, moving the printhead across wiper elements.
Although, there are numerous different types and structures for ink jet printhead cleaning stations, there is constantly a need to improve the overall efficiency of such cleaning systems. Generally, there is a need for improved cleaning systems for use in an ink jet printing apparatus within a postage meter. Specifically there is a need to improve such cleaning systems. One way to improve these cleaning systems in accordance with the present invention is to include wiper elements which wipe ink residue and ink solvent from the printhead more quickly without impacting the throughput rating of the printing unit.
In accordance with the features of one embodiment of the present invention there is provided an inkjet printhead cleaning station comprising in a single housing structure; a first area in which ink is adapted to be forced through nozzles positioned on an inkjet head; a second area including a plurality of wipers adapted to wipe an inkjet head, each of the wipers being mounted on a carriage assembly that is adapted to pivot thereby rotating the wipers and thereby causing edges of the wipers to bend on the housekeeping and scrape off excess ink on the wipers; a third area in which ink is forced through the nozzle for a second time; and a fourth area of the cleaning station in which a cap is positioned on the head to seal nozzles in the printhead.
In accordance with the features of the present invention there is provided another embodiment of the present invention wherein an inkjet head cleaning station for cleaning a movable inkjet printhead assembly comprises a housing structure; a wiper element having a free end portion; a pivotable carriage assembly secured to the wiper element and adapted to rotate the wiper and bend the free end portion of the wiper elements so that ink on the wiper is scraped off by the housing and a book element positioned on the movable inkjet printhead assembly and adapted to engage the pivotable carriage and thereby rotate and bend the free end portion of the wiper against the housing thereby removing ink form the wiper. After rotating the wipers past the bending and scraping obstacle the wipers regain its straight shape and ink is flicked off.